After some investigation by Cosmic Spanner (Mike) and myself I can reveal how to find out.
Firstly you need to know the last two digits of your build code, which you can find here
What you need are the last two digits which are not used to calculate the build date (begins 8). I've noticed on a few P3's the last digit tends to end up printed slightly off the sticker.
+ 83 Code means your car was built at Ryton in Coventry
+ 81 Code means your car was built at Poissy, which is in Paris France.
It seems the the P1's and early P2 were built at Ryton, and the later P2/Rallyes/P3 were built at Poissy. This probably coincides with the change from 306 to 206 production at the Ryton factory. It's not thought that any other GTi-6's/S16 6 Speed were built anywhere else except Ryton & Poissy.
Thanks to Mike this has all been confirmed by a nice guy at Musee Peugeot/PSA
Cherry Red GTi 6